Reflective roadway markers are used by highway departments for delineating highway lines on pavement. Reflective markers are clearly visible at night by reflecting the light from oncoming vehicles back to the vehicle. Generally the markers include a body supporting some sort of a reflective lens.
The U.S. Pat. No. 3,409,344 to Balint et al, issued Nov. 5, 1968 discloses a roadway marker including a housing and reflective inserts, the inserts having substantially flat outer surfaces and a plurality of retro-reflective prisms on the inner surfaces thereof. The inner surfaces of the prisms are coated with a metalized layer and the entire housing is filled with a plastic material to provide strength and rigidity to the marker.
The U.S. Pat. No. 3,332,327 to Heenan, issued July 25, 1967, discloses a pavement marker adapted to be placed on highways. The pavement marker has a front face and is inclined at a predetermined angle to the roadway surface so that a self-cleaning effect is provided by virtue of that predetermined angle.
It has further been found that the angle that the reflective lens makes in relation to the pavement surface also maximizes the reflective efficiency of such a retro-reflective prism surface.
As disclosed in the Heenan '327 patent, as well as the U.S. Pat. No. 4,340,319 to Johnson et al, mechanical abrasion decreases when the angle of the front face of the lens portion of the pavement marker is increased. However, as that angle increases, the cleaning action obtained by tire wiping on the front face of the lens decreases. There is an optimum range for optical effectiveness when the angle of the front face of the lens member is disposed at 30.degree. to the horizontal, with the satisfactory result being obtained where such an angle is between 15.degree. and 45.degree..
It is further noted in the Johnson et al '319 patent that when such pavement markers are used in areas where abrasive materials such as salt are delibertately distributed over the roadway surface during the winter months, the abrasion problem becomes particularly acute. As soft plastic lenses are generally used with fine optical quality, the lenses are highly susceptable to abrasion. Sand and salt are continually brought into contact as the wiping action of the vehicle tires, combined with the abrasive materials, tend to scratch and grind the front face of the lens and diminish optical effectiveness and reflective quality of the pavement marker.
The Johnson et al '319 patent attempts to solve the problem by providing a layer of untempered glass sheet fixedly disposed on the light receiving and refracting portion of the lens. The glass is in compression throughout the expected temperature range to which the pavement marker is exposed and used. The Johnson et al '319 patent utilizes glass because, as is expressly stated in the Johnson et al patent, other coatings on the plastic lens have failed to provide the necessary abrasion resistance or have required curing temperatures which were so high that they distorted the plastic material of the reflector, thereby resulting in a serious deterioration of the reflector optics. Rather than using a polymer system requiring curing, the Johnson et al patent utilizes glass adhered to the lens.
This invention provides another alternative to solving the problem. A polymer coating is chemically bonded to the plastic front face of the lens which provides a hard, smooth surface and does not require high curing temperatures. Rather, this invention provides a polymer system which requires no heat thereby solving the problems of a high temperature cure.